Endemic and atypical Kaposi''s sarcoma in Africa–histopathological aspects

Atypical HIV-associated and endemic Kaposi's sarcoma (KS) differ in their clinical presentation and behaviour. To assess the possible histological differences, a detailed review of 32 cases of atypical KS and 170 cases of endemic KS from sub-Saharan Africa was undertaken. Both forms of KS had similar histological appearances, and evolved through a chronological sequence of patch, plaque and nodule. There was an increase in the proportion of early patch and plaque lesions in cutaneous and mucosal atypical KS (54%) compared with endemic KS (23%). However, nodular lesions were still seen in atypical KS, and formed 56% of the total cases. In addition, atypical KS tended to have more small blood vessels and a lesser degree of inflammatory infiltrate. However, within each of the three stages of the disease, it was not possible to distinguish between the HIV- and non-HIV-related forms.     

Differential expression of c-Met in Kaposi's sarcoma according to progression stage and HIV infection status

Several cytokines, growth factors and the HIV transactivator Tat have been shown to be involved in the pathogenesis of Kaposi's sarcoma (KS). Hepatocyte growth factor/scatter factor (HGF) is an angiogenic cytokine that stimulates proliferation of spindle cells cultured from human KS lesions. The receptor for HGF, the c-Met protein, is expressed by endothelial cells, dermal dendrocytes and KS tumor cells both in vitro and in vivo. KS cells synthesize and secrete HGF and express the hepatocyte growth factor receptor (c-Met), thus providing an autocrine loop for tumor proliferation and neovascularization which can be enhanced by proinflammatory cytokines. We studied the immunohistochemical expression of c-Met in 40 cases of classical Kaposi's sarcoma (C-KS) and AIDS-associated cutaneous Kaposi's sarcoma (AIDS-KS), including 22 plaque stage lesions (12 AIDS-KS cases) and 18 tumor stage lesions (7 AIDS-KS cases). Statistically significant differences in the average intensity of immunohistochemical staining according to the type of lesions progression stages) and the serologic status of the patients were identified. The staining intensity of c-Met was stronger in tumors than in plaques. When only plaques were taken into consideration, the mean staining score was nearly twice as high in C-KS as in AIDS-KS.     

Search for Kaposi's sarcoma-associated virus DNA in hemangioproliferative disorders and cutaneous malignant lymphoma

Recently, a Kaposi's sarcoma-associated herpesvirus (KSHV) was discovered. We evaluated by PCR 14 paraffin-embedded specimens with the histological diagnosis of endemic, classic and HFV-associated Kaposi's sarcoma (KS) for the presence of the KSHV DNA sequence. In addition, biopsies of adjacent, histologically unaffected skin, peripheral-blood mononuclear cells (PBMCs) of HIV-infected KS patients, PBMCs of one classic KS patient, and specimens of patients with hemangioproliferative disorders other than KS as well as samples of cutaneous T-and B-cell lymphoma were analyzed for KSHV. In all cases of KS, independent of the KS subtype, KSHV was detected in lesional skin. No KSHV was found in biopsies of the adjacent unaffected skin or PBMCs of HFV-infected KS patients. We found KSHV in the PBMCs of a patient with classical KS. All specimens of cutaneous T-and B-cell lymphomas or lymphomatoid papulosis were negative for KSHV. In addition, the samples with hemangioproliferative disorders other than KS were negative for KSHV. There was one borderline case of KS or acroangiodermatitis that was positive for KSHV. Additional histological sections and clinical evaluation confirmed the diagnosis of classic KS. In summary, the data indicate that PCR for KSHV should be a useful diagnostic tool in cases of hemangioproliferative disorders.     

Phenotypic characteristics of Kaposi's sarcoma tumour cells derived from patch-, plaque- and nodular-stage lesions: analysis of cell cultures isolated from AIDS and non-AIDS patients and review of the literature

BACKGROUND: Kaposi's sarcoma (KS) is commonly thought to be derived from endothelial cells because of the predominant expression of endothelial markers in KS lesions. However, the heterogeneity of the spindle-cell compartment makes the precise lineage relationship of KS tumour cells unclear. Cultured KS-derived spindle cells constitutively overexpress antiapoptotic proteins and exhibit invasive properties, which suggests that they may adequately represent the tumour cells of KS. OBJECTIVES: We aimed to investigate the expression of a wide variety of immunohistochemical markers by spindle cells derived from patch-, plaque- and nodular-stage lesions from patients with iatrogenic, sporadic and acquired immune deficiency syndrome-related KS, and to review the data reported by other laboratories. METHODS: Cells from six KS cell cultures derived from four subjects were examined by immunostaining. RESULTS: Comparison of these data indicates that KS-derived spindle cells generally express myofibroblast antigens but lack endothelial and/or leucocyte markers. CONCLUSIONS: As the myofibroblast phenotype is not the predominant feature of KS tissues, our findings further substantiate the view that the in vivo dominant endothelial population represents a reactive hyperplasia rather than the true KS tumour process.     

Angiosarcoma arising in a lymphedematous abdominal pannus with histologic features reminiscent of Kaposi's sarcoma: report of a case and review of the literature

BACKGROUND: Despite common endothelial origins, angiosarcoma and Kaposi's sarcoma are clinically and histologically distinct vascular proliferations. The development of angiosarcoma in a chronically edematous abdominal pannus is extremely uncommon. Similarly, tumors with the combined histologic features of angiosarcoma and Kaposi's sarcoma have rarely been described. METHODS: We reviewed the literature on angiosarcoma arising in a lymphedematous abdominal pannus and evaluated an 81-year-old morbidly obese woman who had profound, long-standing edema of the lower abdominal wall in which an aggressive vascular tumor developed. RESULTS: Three clinically similar cases were identified in the literature. All patients were women who generally experienced rapid disease progression. In addition, in our patient, sequential cutaneous sampling from different lesional sites demonstrated disparate histologic changes, ranging from those of classic Kaposi's sarcoma to high-grade angiosarcoma, to areas with combined features of the two tumors. A polymerase chain reaction performed on lesional tissue was negative for human herpesvirus-8 DNA. CONCLUSION: It is important to note that angiosarcoma may develop in the abdomen in association with chronic lymphedema, as demonstrated by the cases noted in this report. In addition, our case highlights the difficulty in differentiating histologically angiosarcoma from Kaposi's sarcoma in some situations, and demonstrates the value of close clinicopathologic correlation and sequential tissue sampling in evaluating problematic cases.     

Kaposi's sarcoma in Nigeria

BACKGROUND: The prevalence of Kaposi's sarcoma (KS) in parts of Africa has been on the increase as a result of the human immunodeficiency virus (HIV) infection pandemic. However, there is a paucity of information for Nigeria. OBJECTIVE: To describe the clinical and epidemiological characteristics of cutaneous KS in patients with HIV-infection in Benin City, Nigeria. METHODS: All patients presenting to the dermatology and infectious diseases clinics of the University of Benin Teaching Hospital, or admitted to its medical wards, within the period July 2000-June 2005 were examined retrospectively in a chart review for KS. Diagnosis of HIV was based upon ELISA testing. The CD4(+) cell counts were performed using the Dyna Bead method and KS was diagnosed histologically. RESULTS: In our survey, 31 patients, representing 0.84% of all new HIV patients seen during the study period, had cutaneous KS. There were 19 males and 12 females, giving a male to female ratio of 1.6 : 1. The mean age was 36.3 +/- 9 years; mean CD4(+) count was 127 +/- 14 cells/dl. The lower limbs (74.2%), trunk (48.4%) and the face (22.6%) were the most frequent sites affected. The lesions were solitary in three patients (9.7%) and multiple in 28 patients (90.3%). CONCLUSION: The prevalence of HIV-related KS is increasing in Nigeria. There is an increase in the number of women being diagnosed with this form of KS, probably owing to more females having HIV disease.     

Acquired immune deficiency syndrome-related hyperkeratotic Kaposi's sarcoma with severe lymphoedema: report of five cases

Kaposi's sarcoma (KS) is the most frequent neoplasm in acquired immune deficiency syndrome (AIDS) patients. Whereas typical cases present as erythematous, plaque or nodular lesions, hyperkeratotic variants of AIDS-associated KS are rare. We describe five patients with AIDS-associated KS with hyperkeratosis and lymphoedema as prominent features. We also speculate on its pathogenesis.     

Recent developments in sexually transmitted diseases: is Kaposi's sarcoma a sexually transmitted disease?

Kaposi's sarcoma (KS), a major complication of AIDS, is found more frequently in the Western hemisphere among homosexual and bisexual male AIDS patients than among other patients with AIDS. Theory and arguments for the possibility of infectious cofactors playing a role in the cause and transmission of the sarcoma are reviewed. While cytomegalovirus, Epstein-Barr, and human herpesvirus have been explored as potential cofactors in AIDS-related KS, the focus here is on the suggestion that Kaposi's sarcoma in a person with AIDS may be caused by an unidentified infectious agent spread through sexual contact. The 1st of 4 arguments supporting this theory is that patients acquiring HIV via sexual contact instead of through parenteral or vertical means experience a much greater risk of KS. 2nd, women acquiring HIV heterosexually from bisexual men experienced a 4 times greater risk of KS than those having other sexual partners. The identification of benign and localized KS in 6 homosexual or bisexual men from New York City without HIV antibodies suggests that the KS causal agent is the same regardless of the presence or absence of HIV infection. There is some evidence that circumstances permitting the heterosexual spread of AIDS in Africa also facilitate the transmission of the KS causal agent. Laboratory and epidemiologic investigations are needed to identify the sexually transmitted cofactor or cause of KS. KS in its classic and endemic African forms is described, followed by discussion of KS and immunodeficiency. 2 sections are then devoted to exploration of AIDS-associated KS in the US and the AIDS-related KS epidemic in Africa, respectively.     

Dermoscopy of Kaposi's sarcoma: Areas exhibiting the multicoloured 'rainbow pattern'

Background  Kaposi's sarcoma is a vascular tumour characterized by a proliferation of spindle cells and endothelial cells to form closely arranged slit-like vascular spaces. Currently, the definitive diagnosis of Kaposi's sarcoma relies on histology. The dermoscopic features of Kaposi's sarcoma are not clearly defined in the scientific literature.
Objectives  We seek to evaluate the dermoscopic features of Kaposi's sarcoma and compare them with other vascular tumours.
Methods  One hundred forty-one lesions from seven patients with histologically proven Kaposi's sarcoma were evaluated using polarized light dermoscopy for the presence of various dermoscopic features. Twenty patients with other vascular tumours were also examined.
Results  Dermoscopic examination revealed bluish-reddish coloration (84% of lesions), multicoloured areas showing various colours of the rainbow spectrum (36%), scaly surface (29%), and small brown globules (15%). The 'rainbow pattern' was found in six out of seven patients with Kaposi's sarcoma and was not observed in other vascular tumours. In addition, there was an absence of dermoscopic features specific for other vascular and non-vascular skin tumours, such as well-defined lacunae or structured vascular pattern, in most of the Kaposi's sarcoma lesions.
Conclusions  The most frequent dermoscopic patterns in Kaposi's sarcoma were found to be bluish-reddish coloration, the 'rainbow pattern', and scaly surface. The rainbow pattern is a dermoscopic feature which has not been previously described. We propose that dermoscopy, as an adjunct to clinical examination, may enhance accuracy in the preoperative diagnosis of Kaposi's sarcoma.     

Lymphangioma-like Kaposi sarcoma

BACKGROUND: Lymphangioma-like Kaposi's sarcoma (LLKS) is a rare morphologic expression of Kaposi's sarcoma (KS) that occurs in virtually all of the well-recognized clinical subtypes of the disease and has the potential to mimic other pathologic processes. In this study, we present the clinical and pathological features of four patients with LLKS. METHODS: Four cases of LLKS were retrieved from the dermatopathology files of our institution. All four tumours were tested immunohistochemically with anti-human herpesvirus-8 (HHV-8) latent nuclear antigen-1 (LNA-1) and anti-CD34 antibodies. RESULTS: Clinically, each patient presented with violaceous patches, papules or plaques; one patient presented with bullous lesions. All of the LLKS biopsy specimens revealed areas with characteristic light microscopic features of KS. Lymphangioma-like foci consisted of ectatic, irregularly shaped vascular spaces lined by mildly atypical endothelial cells. All tumour cells, including those associated with LLKS foci, showed a strong and diffuse reactivity for anti-HHV-8 LNA-1 and anti-CD34. KS progressed slowly in two patients with adequate follow-up. CONCLUSIONS: As LLKS can mimic other disease processes, the correct diagnosis relies heavily on the recognition of salient clinical and histological features of conventional KS, including a strong immunohistochemical expression of HHV-8-associated LNA-1 in lesional cells.     

Matrix metalloproteinases in the progression and regression of Kaposi's sarcoma

BACKGROUND: Matrix metalloproteinases (MMPs) are associated with Kaposi's sarcoma (KS) tumorigenesis. To date, only a few MMPs have been studied in KS lesions. Their role in KS regression has not been investigated. The aim of this study was to evaluate the expression of multiple MMPs in developing and pharmacologically regressed KS lesions. METHODS: Nine samples of acquired immune deficiency syndrome (AIDS)-related and classic cutaneous KS lesions at various histological stages were studied. Regressing KS lesions from three patients treated with systemic therapy were procured after one and two cycles of chemotherapy. Tissue sections from all specimens were immunostained using monoclonal antibodies to MMP-1, MMP-2, MMP-3, MMP-7, MMP-9, MMP-13, and MMP-14. RESULTS: KS lesional cells were immunoreactive for all MMPs, except MMP-14. Admixed inflammatory cells were immunoreactive for MMP-1, MMP-2, MMP-7, MMP-9, and MMP-13. The MMP immunoprofile in residual KS lesional cells was unaltered in regressed lesions. Increased extracellular matrix (ECM) and macrophage immunoreactivity for MMPs was identified in regressed specimens. CONCLUSIONS: These data show that developing KS lesional cells express collagenases (MMP-1, MMP-13), gelatinases (MMP-2, MMP-9), stromelysin-1 (MMP-3), and matrilysin (MMP-7) but not the membrane-type MMP-14. This MMP expression profile is retained by residual KS cells and also expressed by infiltrating macrophages in regressed KS lesions. Pantanowitz L, Dezube BJ, Hernandez-Barrantes S, Tahan SR, Dabbous MK. Matrix metalloproteinases in the progression and regression of Kaposi's sarcoma.     

HHV-8/KSHV during the development of Kaposi's sarcoma: evaluation by polymerase chain reaction and immunohistochemistry

The human gamma-herpes virus-8 (HHV-8) was first described in AIDS-related Kaposi's sarcoma (KS) tumour samples. In this study, we report comparative studies on paraffin-embedded biopsies of AIDS-related KS (AKS) and endemic KS (EKS) with regard to HHV-8 content as evaluated using polymerase chain reaction (PCR) and immunohistochemistry. DNA was extracted either using Chelex-100 or using Qia-gene kit and was evaluated with the help of a semiquantitative PCR assay. The PCR detection of HHV-8 was more sensitive to the Chelex method than to Qia-gene. The threshold for PCR test sensitivity with the help of serial dilution of DNA was at the level of five plasmid ORF-26 regions, and DNA from 25 body cavity-based lymphoma-1 cells. The results expressed as virus load/actin unit showed progressively higher HHV-8 levels in late (nodular) cases, compared to those in early (patch/plaque) stages. Evaluation of HHV-8 DNA levels in tumour tissues, thus, indicates a correlation between virus load and KS stage. Double immunostaining of spindle cells (SC) in KS biopsies for CD34 and HHV-8/latency-associated nuclear antigen (LANA) showed an increase in double-positive SC in the lesions of nodular AKS and EKS cases, compared to that in plaque and patch stages. However, 10-15% of CD34+/LANA- SC cells were observed during the development from patch to nodular cases of AKS and EKS. Our results indicate that PCR analysis is a simple and sensitive diagnostic method for HHV-8 evaluation in KS tissues, processed for conventional histopathology.     

Kaposi's sarcoma and other manifestations of human herpesvirus 8

Kaposi's sarcoma (KS) was described by Moritz Kaposi in 1872 and was known for an entire century as a rare disorder of older men usually of Eastern European, Mediterranean, and/or Jewish origin. In the early 1980s, the prevalence of KS began to increase dramatically and soon became the most common malignancy in patients with AIDS, especially those who were male homosexuals. In 1994, a new human herpesvirus (HHV) was found to be present in almost 100% of KS lesions. This virus was found to be a gammaherpesvirus, closely related to Epstein-Barr virus, and was designated HHV-8. Subsequently, HHV-8 DNA was found in almost all specimens of classic KS, endemic KS, and iatrogenic KS, as well as epidemic KS (ie, AIDS KS). It is now believed that HHV-8 is necessary, but not sufficient, to cause KS and that other factors such as immunosuppression play a major role. The use of highly active antiretroviral therapy (HAART) since 1996 has markedly reduced the prevalence of AIDS KS in western countries, but because 99% of the 40 million patients with AIDS in the world cannot afford HAART, KS is still a very common problem. Primary effusion lymphoma and multicentric Castleman's disease are also thought to be due to HHV-8. Although HHV-8 DNA has been described in a number of other cutaneous disorders, there is little evidence that HHV-8 is of etiologic significance in these diseases. The mechanism by which HHV-8 causes KS, primary effusion lymphoma, and multicentric Castleman's disease is not well understood but is thought to involve a number of molecular events, the study of which should further our understanding of viral oncology. (J Am Acad Dermatol 2002;47:641-55.) Learning objective: At the completion of this learning activity, participants should be familiar with Kaposi's sarcoma and other manifestations of human herpesvirus 8.     

Study of HHV-8 DNA sequences in archival biopsies from lesional skin of Kaposi's sarcoma,various mesenchymal tumors and related reactive conditions

Background: HHV-8 has been identified as the causative agent of Kaposi's sarcoma (KS) and some lymphoproliferative disorders. In addition, there are anecdotal reports on the presence of HHV-8 in other tumors, especially cutaneous epithelial and mesenchymal neoplasms. The aim of the study was to ascertain the value of identification of HHV-8 viral DNA sequences in routinely processed, formalin-fixed, paraffin-embedded tissues for the diagnosis of Kaposi's sarcoma and other mesenchymal tumors.
Methods: The presence of HHV-8 sequences in archival material was studied by nested PCR using specific primers for amplification of a 233-bp long fragment of HHV-8 (ORF 26).
Results: Thirty-three patients with KS (18 classic/sporadic, six post-transplant and nine AIDS-related) and various mesenchymal tumors and related conditions (n = 76) were studied. HHV-8 DNA sequences were detected in 29 of the 33 cases of KS and in one case of multiple eruptive dermatofibroma (MEDF).
Conclusions: Identification of HHV-8 DNA sequences in routinely processed tissue is a useful diagnostic marker for KS. Although other mesenchymal tumors are usually not associated with HHV-8, its presence is not fully specific for KS since HHV-8 sequences were also found in one case of MEDF. Therefore, PCR analysis for the detection of HHV-8 should only be used as an additional diagnostic marker for KS and in the context of other tools such as routine histology.     

The influence of highly active antiretroviral therapy on AIDS-associated Kaposi's sarcoma

To assess the clinical and biological benefit of highly active antiretroviral therapy on AIDS-associated Kaposi's sarcoma (KS), 13 patients with AIDS-associated Kaposi's sarcoma (five pulmonary KS and eight cutaneous KS) were prospectively followed for a mean duration of 12 months. Six patients were treated with specific anti-KS chemotherapy before or simultaneously with the introduction of antiretroviral therapy. Clinical response was assessed according to the AIDS Clinical Trial Group (ACTG) criteria. CD4 cell counts, plasma HIV-1 RNA and human herpesvirus 8 (HHV-8) viraemia were measured at baseline and at different points. Among patients with pulmonary KS, we observed three complete responses (CR), one partial response (PR) and one progression. The median survival time after the diagnosis of pulmonary KS was 15 months with a median duration of the response after the discontinuation of specific chemotherapy for KS of 8 months. Among patients with cutaneous KS, we observed four CR, three PR and one stable response. A complete response was significantly associated with a reversal in HHV-8 viraemia (five of six vs. one of six; P = 0.02, Mann-Whitney test).     

Histological characterization of regression in acquired immunodeficiency syndrome-related Kaposi's sarcoma

BACKGROUND: Kaposi's sarcoma (KS) is an angioproliferative lesion that may regress or progress. Progression is related to spindle cell proliferation and the expression of human herpes virus-8 latency genes, including latent nuclear antigen-1 (LNA-1), cyclin-D1, and bcl-2. KS regression has not been well characterized histologically. Therefore, this study was undertaken to characterize the histopathology of pharmacologically induced regressed cutaneous KS. METHODS: Skin punch biopsies from eight patients with acquired immunodeficiency syndrome (AIDS)-related KS, that regressed following chemotherapy with paclitaxel or the angiogenesis inhibitor Col-3, were investigated by light microscopy. Comparative immunophenotyping on pre- and post-treatment specimens for CD31, LNA-1, cyclin-D1, bcl-2, and CD117 (c-kit) was performed. RESULTS: Clinical and histologic features of regression were similar for paclitaxel and Col-3 treatment. On clinical examination, lesions flattened, became smaller, and lost their purple-red appearance, resulting in an orange-brown macule. Histological regression was divided into partial (n = 3) and complete (n = 5) regression. Partially regressed lesions had a significant reduction of spindle cells in the dermal interstitium, with residual spindle cells arranged around superficial and mid-dermal capillaries. Complete regression was characterized by an absence of detectable spindle cells, with a slight increase in capillaries of the superficial plexus. All regressed samples exhibited a prominent, superficial, perivascular, lymphocytic infiltrate and abundant dermal hemosiderin-laden macrophages. This clinicopathologic picture resembled the findings of pigmented purpura. CD31 staining correlated with the reduction of spindle cells. Regression was accompanied by a quantitative and qualitative decrease in LNA-1 and cyclin-D1 immunoreactivity, but no change in bcl-2 or c-kit expression. CONCLUSIONS: Pharmacologically induced regression of AIDS-related cutaneous KS is characterized by a complete loss or decrease of spindle cells, increased lymphocytes, and prominent dermal siderophage deposition. Without any prior knowledge of the history of KS regression following therapy, regressed KS lesions may be misdiagnosed clinically and histologically as pigmented purpuric dermatitis.     

长链非编码RNA在Kaposi肉瘤组织中的表达

目的：检测长链非编码RNA(lncRNA)在Kaposi肉瘤组织和瘤旁正常组织中的表达。方法：利用高通量lncRNA芯片技术检测5例Kaposi肉瘤组织及其瘤旁正常组织的lncRNA 表达谱,筛选差异表达的lncRNA,并利用实时荧光定量PCR(qRT-PCR)方法进一步验证芯片结果,同时采用生物信息学分析差异lncRNA靶基因KEGG通路注释。结果：与正常组织相比,Kaposi肉瘤组织中共筛选出717个差异表达的lncRNA,其中上调表达408个,下调表达309个;与正常组织相比,lnc-PXDN-3:3和lnc-PERP-10:2在Kaposi肉瘤组织中均表达上调,与芯片结果一致。生物学过程注释集中在Wnt信号通路、泛素化代谢、TGF-beta信号通路、P53信号通路。结论：lncRNA可能与Kaposi肉瘤发病有关。     

Rainbow pattern in Kaposi's sarcoma under polarized dermoscopy: a dermoscopic pathological study

Summary Background We found previously that the features of Kaposi’s sarcoma (KS) under polarized dermoscopy are characterized by a bluish‐reddish coloration, a scaly surface, small brown globules and, most distinctively, the multicoloured ‘rainbow pattern’. Objectives To evaluate the significance of the rainbow pattern on dermoscopy as a diagnostic feature in KS, and to demonstrate that it is associated with the unique vascular structure of the tumour. Methods More than 100 lesions from seven patients with histologically proven KS were examined with polarized light dermoscopy. Sixty‐three patients with various other cutaneous vascular and nonvascular tumours were also examined. KS lesions exhibiting the rainbow pattern and KS lesions lacking the rainbow pattern on dermoscopy were excised, and dermoscopic features were compared with histopathological structures. The dermoscopic patterns of other vascular tumours were also compared with histological features. In addition, the changes in dermoscopic features and histological structures were assessed before and after surgical therapy in one patient with KS. Results On the basis of evaluations with polarized dermoscopy, the rainbow pattern was found to be a highly specific dermoscopic feature for KS. Histology of KS lesions showing the rainbow pattern under polarized light dermoscopy demonstrated a vascular lumen‐rich pattern of closely arranged ‘back‐to‐back’ vascular structures, whereas histology of KS lesions without the rainbow pattern showed a vascular lumen‐poor pattern with vascular lumina separated further apart by intervening stromal and cellular tissue. Other vascular tumours did not exhibit the rainbow pattern and were characterized histologically by variably sized vascular structures separated by substantial amounts of stromal and cellular tissue. In one patient with KS, disappearance of the rainbow pattern was associated with obliteration of the vascular structure following surgical ablation therapy. Conclusions The rainbow pattern in KS is associated with the vascular lumen‐rich histological subtype, is not manifest in the vascular lumen‐poor subtype and disappears following total tumour removal. Therefore, the underlying structural arrangement of the vessels in KS may determine whether or not the rainbow pattern can be seen on polarized dermoscopy.